The present invention relates to methods for treating subterranean formations. More particularly, in certain embodiments, the present invention relates to methods of using in subterranean applications treatment fluids that comprise a transient polymer network.
In today's downhole technology, a large portion of the wells have been completed at depths of greater than 15,000 ft, and as a result, most previously designed treatment fluids and additives that were designed for more shallow wells may not perform adequately at temperatures and at pressures commonly associated with wells of greater depths. Wells at depths exceeding 15,000 ft often involve higher temperatures and pressures, necessitating the need for fluids and additives that will perform at these depths. In addition to the high temperatures and pressures, wells completed at these depths often produce fluids like carbon dioxide (CO2) or hydrogen sulfide (H2S).
Polymeric agents, such as cationic polymers, high molecular weight polyacrylamide polymers, polysaccharides, synthetic polymers, and the like, have previously been added to treatment fluids to obtain the desired properties for a variety of subterranean treatments. Such treatments include, but are not limited to, drilling, stimulation treatments (e.g., fracturing treatments, acidizing treatments), and completion operations (e.g., sand control treatments like gravel packing). As used herein, the term “treatment,” or “treating,” refers to any subterranean operation that uses a fluid in conjunction with a desired function and/or for a desired purpose. The term “treatment,” or “treating,” does not imply any particular action by the fluid or any particular component thereof.
Traditional treatment fluids may be grouped into two classifications. Such classifications include oil-based treatment fluids and aqueous-based treatment fluids. In the past, oil-based treatment fluids are thought to have some superior performance characteristics over aqueous-based treatment fluids. However, aqueous-based treatment fluids may be more economical to use and less damaging to the formation and to the environment.
One reason that oil-based treatment fluids are thought to have desirable characteristics is that they are better at maintaining sufficient shale inhibition. Proper shale inhibition is important in preventing wellbore instability. Aqueous-based treatment fluids often give rise to insufficient shale inhibition when such fluids are used in water-sensitive formations. The resultant swelling of the clays may give rise to solid-laden treatment fluids that are pumped at decreased speeds leading to the poor performance of water-based treatment fluids. In addition, the clays can damage the equipment used in a subterranean operation and slow down the overall effectiveness of the operation. In extreme scenarios, the clays may seal off a portion of the formation leading to loss of production. Another problem associated with aqueous-based treatment fluids is their incompatibility with heavy brines.
An important consideration for assessing the utility of a treatment fluid for a given purpose may include the fluid's Theological parameters. For use as a subterranean treatment fluid, a fluid generally should be capable of maintaining certain viscosities suitable for the desired operation. For example, a drilling fluid preferably has sufficiently viscosity to be capable of supporting and carrying the drill cuttings to the surface without being so viscous as to interfere with the drilling operation. Increased viscosity can result in problematic sticking of the drill string, and increased circulating pressures can contribute to lost circulation problems in the formation. Clays are commonly used as a way to maintain sufficient viscosity in such treatment fluids. These clays may typically require vigorous agitation in the fluid to reach a fully active state and provide an increase in viscosity. Time pressures may demand that fluids be prepared quickly for shipment to the drilling operation. As a result, inadequate shear and over-treatment may occur when using clays.
Aqueous treatment fluids which do not contain organophilic clays may offer many advantages if they can retains the performance of an oil-based treatment fluid while maintaining the many of the benefits of using an aqueous-based treatment fluid.